Objective lens assemblies may be incorporated into a number of devices, such as night vision devices or other optical systems. Each lens assembly typically includes an objective lens cell and a housing, where the objective lens cell is inserted in a tubular section of the housing. A set of female threads on the inner tubular section of the housing mates corresponding male threads on the outer surface of the lens cell. By translating the objective lens cell relative to the housing, along an optical axis, the objective lens assembly focuses upon an external subject. The threaded coupling between the objective lens cell and the housing has a tolerance sufficient to allow for a loose fit between the threads.
Because of the need for a loose fit between the mated threads, the coupling between the housing and the lens cell introduces backlash. Backlash is the free play that exists between coupled elements, which may be measured as the distance in which one element is displaced before any movement is imparted to the other element in the coupling. The backlash displaces the lens cell along the optical axis until a thread of the lens cell engages an adjacent thread of the housing. Backlash causes focus and resolution errors in the objective lens assembly which may require disassembly and repair.
It would thus be beneficial to provide a device to reduce backlash in objective lens assemblies. The present invention provides a biasing device to reduce backlash, as will be described below.